On Mon, Nov 6, 2017 at 1:54 PM, Emilio G. Cota <c...@braap.org> wrote:
> On Mon, Nov 06, 2017 at 12:10:22 -0200, Eduardo Habkost wrote:
>> On Fri, Nov 03, 2017 at 06:24:07PM -0400, Emilio G. Cota wrote:
>> > /**
>> > * MachineClass:
>> > * @max_cpus: maximum number of CPUs supported. Default: 1
>> > + * @force_max_cpus: if set, force the global max_cpus to match @max_cpus
>> > * @min_cpus: minimum number of CPUs supported. Default: 1
>> > * @default_cpus: number of CPUs instantiated if none are specified.
>> > Default: 1
>> > * @get_hotplug_handler: this function is called during bus-less
>>
>> If we have a field containing the default value for smp_cpus
>> (default_cpus), what about a default_max_cpus field for the
>> default value of max_cpus? This could make the rules a bit
>> easier to follow.
>>
>> (But I wonder if there's a way we can do this without introducing
>> another MachineClass field and making the initialization code
>> more complex.)
>
> I don't think the rules are too hard to follow, since they're trivial
> for most machines because the defaults are reasonable (i.e. they
> only set max_cpus, and everything else is set to 1). Some machines
> though are tricky in what can and cannot support, e.g. the Xilinx
> ones we've been dealing with in this thread.
>
> wrt .default_max_cpus instead of .force_max_cpus: it lets users
> shoot themselves in the foot, so I wouldn't go this route.
> For instance, what do we do if the user passes maxcpus < default_max_cpus?
> max_cpus would be set to maxcpus, yet they could still pass the
> -global override that instantiates two extra CPUs, and at that point
> we'd fail (in TCG) without providing a meaningful error.
>
> We could increase maxcpus to default_max_cpus, but at that point
> default_max_cpus becomes the same thing as force_max_cpus (!).
>
> An alternative I've come up with is to have a field that specifies how
> many CPUs could be created in addition to those specified in max_cpus
> (in the Xilinx case these would be the RPUs). Patch below.
>
>> The fact that MachineClass::max_cpus and the 'max_cpus' globals
>> have completely different meanings makes this confusing enough.
>> Maybe we should rename the 'max_cpus' global variable to
>> 'max_hotplug_cpus'.
>
> I have no trouble with their different meanings, although I admit
> I am now quite well acquainted with this code so my bias is strong :-)
>
> Thanks,
>
> Emilio
>
> ---8<---
>
> Subject: [PATCH] hw: add .{additional_max,min,default}_cpus fields to
> machine_class
>
> max_cpus needs to be an upper bound on the number of vCPUs
> initialized; otherwise TCG region initialization breaks.
>
> Some boards initialize a hard-coded number of vCPUs, which is not
> captured by the global max_cpus. Fix it by adding the .min_cpus
> field to machine_class.
>
> A subset of those boards can also instantiate additional vCPUs
> beyond what is specified in -smp, e.g. via -global overrides. To
> ensure that max_cpus remains an upper bound on the number of vCPUs
> that can be instantiated, we also add the .additional_max_cpus field
> to machine_class.
>
> This commit also changes some user-facing behaviour: we now die if
> -smp is below this hard-coded vCPU minimum instead of silently
> ignoring the passed -smp value (sometimes announcing this by printing
> a warning). However, the introduction of .default_cpus lessens the
> likelihood that users will notice this: if -smp isn't set, we now
> assign the value in .default_cpus to both smp_cpus and max_cpus. IOW,
> if a user does not set -smp, they always get a correct number of vCPUs.
>
> This change fixes 3468b59 ("tcg: enable multiple TCG contexts in
> softmmu", 2017-10-24), which broke TCG initialization for some
> ARM boards.
Sorry for the silence here, I noticed these were broken just before I
went on holidays but didn't get a chance to fix anything.
For the Xilinx case I was thinking of patching the machine code to
sanely follow the -smp option.
-smp 1 -> Only create 1 A53
-smp 4 -> Create 4 A53s
-smp 6 -> Create all the CPUs
I see a lot of advantages in not forcing the smallest number of CPUs
to be 4 unless we really have to.
I do see a nice advantage in being able to set the default smp option
to something not 1 so the default closely matches hardware, but users
can override that if they want to.
So for the patch below I like the default_cpus option, but for Xilinx
at least I would like to patch the logic to follow the -smp option
instead of force a minimum.
Thanks,
Alistair
>
> Fixes: 3468b59e18b179bc63c7ce934de912dfa9596122
> Reported-by: Thomas Huth <th...@redhat.com>
> Suggested-by: Peter Maydell <peter.mayd...@linaro.org>
> Signed-off-by: Emilio G. Cota <c...@braap.org>
> ---
> hw/arm/exynos4_boards.c | 12 ++++--------
> hw/arm/raspi.c | 2 ++
> hw/arm/xlnx-zcu102.c | 9 ++++++++-
> include/hw/boards.h | 10 ++++++++++
> vl.c | 38 +++++++++++++++++++++++++++++++++++---
> 5 files changed, 59 insertions(+), 12 deletions(-)
>
> diff --git a/hw/arm/exynos4_boards.c b/hw/arm/exynos4_boards.c
> index f1441ec..750162c 100644
> --- a/hw/arm/exynos4_boards.c
> +++ b/hw/arm/exynos4_boards.c
> @@ -27,7 +27,6 @@
> #include "qemu-common.h"
> #include "cpu.h"
> #include "sysemu/sysemu.h"
> -#include "sysemu/qtest.h"
> #include "hw/sysbus.h"
> #include "net/net.h"
> #include "hw/arm/arm.h"
> @@ -129,13 +128,6 @@ exynos4_boards_init_common(MachineState *machine,
> Exynos4BoardType board_type)
> {
> Exynos4BoardState *s = g_new(Exynos4BoardState, 1);
> - MachineClass *mc = MACHINE_GET_CLASS(machine);
> -
> - if (smp_cpus != EXYNOS4210_NCPUS && !qtest_enabled()) {
> - error_report("%s board supports only %d CPU cores, ignoring smp_cpus"
> - " value",
> - mc->name, EXYNOS4210_NCPUS);
> - }
>
> exynos4_board_binfo.ram_size = exynos4_board_ram_size[board_type];
> exynos4_board_binfo.board_id = exynos4_board_id[board_type];
> @@ -189,6 +181,8 @@ static void nuri_class_init(ObjectClass *oc, void *data)
> mc->desc = "Samsung NURI board (Exynos4210)";
> mc->init = nuri_init;
> mc->max_cpus = EXYNOS4210_NCPUS;
> + mc->min_cpus = EXYNOS4210_NCPUS;
> + mc->default_cpus = EXYNOS4210_NCPUS;
> mc->ignore_memory_transaction_failures = true;
> }
>
> @@ -205,6 +199,8 @@ static void smdkc210_class_init(ObjectClass *oc, void
> *data)
> mc->desc = "Samsung SMDKC210 board (Exynos4210)";
> mc->init = smdkc210_init;
> mc->max_cpus = EXYNOS4210_NCPUS;
> + mc->min_cpus = EXYNOS4210_NCPUS;
> + mc->default_cpus = EXYNOS4210_NCPUS;
> mc->ignore_memory_transaction_failures = true;
> }
>
> diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
> index 5941c9f..cd5fa8c 100644
> --- a/hw/arm/raspi.c
> +++ b/hw/arm/raspi.c
> @@ -167,6 +167,8 @@ static void raspi2_machine_init(MachineClass *mc)
> mc->no_floppy = 1;
> mc->no_cdrom = 1;
> mc->max_cpus = BCM2836_NCPUS;
> + mc->min_cpus = BCM2836_NCPUS;
> + mc->default_cpus = BCM2836_NCPUS;
> mc->default_ram_size = 1024 * 1024 * 1024;
> mc->ignore_memory_transaction_failures = true;
> };
> diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
> index e2d15a1..0f1837e 100644
> --- a/hw/arm/xlnx-zcu102.c
> +++ b/hw/arm/xlnx-zcu102.c
> @@ -185,6 +185,10 @@ static void xlnx_ep108_machine_class_init(ObjectClass
> *oc, void *data)
> mc->block_default_type = IF_IDE;
> mc->units_per_default_bus = 1;
> mc->ignore_memory_transaction_failures = true;
> + mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> + mc->max_additional_cpus = XLNX_ZYNQMP_NUM_RPU_CPUS;
> + mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> + mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> }
>
> static const TypeInfo xlnx_ep108_machine_init_typeinfo = {
> @@ -240,7 +244,10 @@ static void xlnx_zcu102_machine_class_init(ObjectClass
> *oc, void *data)
> mc->block_default_type = IF_IDE;
> mc->units_per_default_bus = 1;
> mc->ignore_memory_transaction_failures = true;
> - mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
> + mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> + mc->max_additional_cpus = XLNX_ZYNQMP_NUM_RPU_CPUS;
> + mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> + mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
> }
>
> static const TypeInfo xlnx_zcu102_machine_init_typeinfo = {
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 191a5b3..be582dd 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -102,6 +102,13 @@ typedef struct {
>
> /**
> * MachineClass:
> + * @max_cpus: maximum number of CPUs supported. Default: 1
> + * @max_additional_cpus: # of CPUs that can be instantiated in addition to
> those
> + * instantiated with -smp. For instance, if a machine has 4 main CPUs and
> 2
> + * optional CPUs (e.g. instantiated via -global overrides), then @max_cpus
> + * and @max_additional_cpus will be set to 4 and 2, respectively.
> Default: 0
> + * @min_cpus: minimum number of CPUs supported. Default: 1
> + * @default_cpus: number of CPUs instantiated if none are specified.
> Default: 1
> * @get_hotplug_handler: this function is called during bus-less
> * device hotplug. If defined it returns pointer to an instance
> * of HotplugHandler object, which handles hotplug operation
> @@ -167,6 +174,9 @@ struct MachineClass {
> BlockInterfaceType block_default_type;
> int units_per_default_bus;
> int max_cpus;
> + int max_additional_cpus;
> + int min_cpus;
> + int default_cpus;
> unsigned int no_serial:1,
> no_parallel:1,
> use_virtcon:1,
> diff --git a/vl.c b/vl.c
> index ec29909..e3ee36e 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -160,8 +160,8 @@ Chardev *virtcon_hds[MAX_VIRTIO_CONSOLES];
> Chardev *sclp_hds[MAX_SCLP_CONSOLES];
> int win2k_install_hack = 0;
> int singlestep = 0;
> -int smp_cpus = 1;
> -unsigned int max_cpus = 1;
> +int smp_cpus;
> +unsigned int max_cpus;
> int smp_cores = 1;
> int smp_threads = 1;
> int acpi_enabled = 1;
> @@ -4330,12 +4330,44 @@ int main(int argc, char **argv, char **envp)
> smp_parse(qemu_opts_find(qemu_find_opts("smp-opts"), NULL));
>
> machine_class->max_cpus = machine_class->max_cpus ?: 1; /* Default to UP
> */
> + machine_class->min_cpus = machine_class->min_cpus ?: 1;
> + machine_class->default_cpus = machine_class->default_cpus ?: 1;
> +
> + /* if -smp is not set, default to mc->default_cpus */
> + if (!smp_cpus) {
> + smp_cpus = machine_class->default_cpus;
> + max_cpus = machine_class->default_cpus;
> + }
> +
> + /* sanity-check smp_cpus and max_cpus */
> + if (smp_cpus < machine_class->min_cpus) {
> + error_report("Invalid SMP CPUs %d. The min CPUs "
> + "supported by machine '%s' is %d", smp_cpus,
> + machine_class->name, machine_class->min_cpus);
> + exit(1);
> + }
> if (max_cpus > machine_class->max_cpus) {
> - error_report("Invalid SMP CPUs %d. The max CPUs "
> + error_report("Invalid max SMP CPUs %d. The max CPUs "
> "supported by machine '%s' is %d", max_cpus,
> machine_class->name, machine_class->max_cpus);
> exit(1);
> }
> + if (max_cpus < machine_class->min_cpus) {
> + error_report("Invalid max SMP CPUs %d. The min CPUs "
> + "supported by machine '%s' is %d", max_cpus,
> + machine_class->name, machine_class->min_cpus);
> + exit(1);
> + }
> +
> + /*
> + * Some boards can instantiate additional CPUs, e.g. by overriding
> + * device params via -global arguments. Update max_cpus so that
> + * we are sure to have an upper bound on the maximum number of
> + * vCPUs that might be instantiated.
> + */
> + if (machine_class->max_additional_cpus) {
> + max_cpus += machine_class->max_additional_cpus;
> + }
>
> /*
> * Get the default machine options from the machine if it is not already
> --
> 2.7.4
>
>
